Spatial light modulation (SLM) display systems are display systems that use light reflected or transmitted by individual elements of a spatial light modulator to generate a display image. One type of spatial light modulator is a digital micromirror device (DMD). SLM display systems are known that incorporate a DMD, such as those commercially available from Texas Instruments, Inc. under the trademark DLP™ (Digital Light Processing).
FIG. 1 shows an example of an SLM projection display system 10. The system 10 includes an arc lamp 11 that emits white light. A first condenser lens 13 focuses the white light onto a color filter wheel 15. A second condenser lens 17 receives the filtered light and focuses it onto a DMD chip 19. The DMD chip 19 includes an array of tiny mirror elements, which together modulate the light and transmit the modulated light to projection lens 29, where it can be focused for display on the screen 31.
FIG. 2 shows a portion of a DMD array 19 having mirror elements 21 suspended over a substrate 23. Electrostatic attraction between the mirror 21 and an address electrode 25 causes the mirror 21 to twist or pivot, in either of two directions, about an axis formed by a pair of torsion beam hinges 27a and 27b. Typically, the mirror 21 rotates about these hinges until the rotation is mechanically stopped. The movable mirror 21 tilts into the on or off states by electrostatic forces depending on the data written to an associated memory cell (not shown). The tilt of the mirror 21 can be on the order of plus 10 degrees (on) or minus 10 degrees (off) to modulate the light that is incident on the mirrored surface. For additional details, see U.S. Pat. No. 5,061,049 entitled “Spatial Light Modulator” and U.S. Pat. No. 5,280,277 entitled “Field Updated Deformable Mirror Device,” both to Larry J. Hornbeck.
Referring again to FIG. 1, the color filter wheel 15 includes red (R), green (G), and blue (B) filter elements. The filter wheel 15 is driven by a motor 16 to rotate so that the different color filter elements sequentially filter the light passing through the filter wheel 15. Thus, as the filter wheel 15 rotates, the color of light emanating from the filter wheel 15 changes according to the wheel position. Typically the filter wheel 15 rotates at least once per frame for display of a multi-color image. The frequency of the rotation of the wheel 15 is controlled by a sequencer 33 based on the frame rate of image data received from an image source 35.